At a car-boot sale near Derby, a radio producer bought a dusty hoard of audio tapes along with a heavy old tape recorder. Coaxing the machine back to life, he discovered the jettisoned archive of a group of audio amateurs who made, played and swapped recordings in the 1960s and 70s, when domestic tape-recording was in its infancy-and before the audio cassette had conquered the world. Producer Mark Vernon